18 Corps, 18th Corps, Eighteenth Corps, or XVIII Corps may refer to:
- 18th Army Corps (France)
- XVIII Army Corps (Wehrmacht), a unit of the German Army
- XVIII Corps (German Empire)
- XVIII Reserve Corps (German Empire)
- XVIII Corps (Ottoman Empire)
- XVIII Corps (United Kingdom)
- XVIII Airborne Corps, United States
- XVIII Corps (Union Army), a unit in the American Civil War